This invention relates, inter alia, to novel compositions of matter useful, inter alia, as cocatalysts, to novel catalyst compositions made using such cocatalysts, to methods for preparing these catalysts, and to methods for polymerization utilizing the catalysts.
The use of soluble Ziegler-Natta type catalysts in the polymerization of olefins is well known in the prior art. In general, such systems include a Group 4 metal compound and a metal or metalloid alkyl cocatalyst, such as aluminum alkyl cocatalyst. More broadly, it may be said to include a mixture of a Group 1, 2 or 13 metal alkyl and a transition metal complex from Group 4-5 metals, particularly titanium, zirconium, or hafnium with aluminum alkyl cocatalysts.
First generation cocatalyst systems for homogeneous metallocene Ziegler-Natta olefin polymerization, alkylaluminum chlorides (AlR.sub.2 Cl), exhibit low ethylene polymerization activity levels and no propylene polymerization activity. Second generation cocatalyst systems, utilizing methyl aluminoxane (MAO), raise activities by several orders of magnitude. In practice however, a large stoichiometric excess of MAO over catalyst ranging from several hundred to ten thousand must be employed to have good activities and stereoselectivities. Moreover, it has not been possible to isolate characterizable metallocene active species using MAO. The third generation of cocatalyst, B(C.sub.6 F.sub.5).sub.3, proves to be far more efficient while utilizing a 1:1 catalyst-cocatalyst ratio. Although active catalyst species generated with B(C.sub.6 F.sub.5).sub.3 are isolable and characterizable, the anion MeB(C.sub.6 F.sub.5).sub.3.sup..crclbar., formed after Me.sup..crclbar. abstraction from metallocene dimethyl complexes, is weakly coordinated to the electron-deficient metal center, thus resulting in a drop of certain catalytic activities. The recently developed B(C.sub.6 F.sub.5).sub.4.sup..crclbar. type of non-coordinating anion exhibits some of the highest reported catalytic activities, but such catalysts have proven difficult to obtain in the pure state due to poor thermal stability and poor crystallizability, which is crucial for long-lived catalysts and for understanding the role of true catalytic species in the catalysis for the future catalyst design. Synthetically, it also takes two more steps to prepare such an anion than for the neutral organo-Lewis acid.
In our prior applications referred to hereinabove, and in publications appearing in J. Am. Chem. Soc. 1996, 118, 12451-12452, Organometallics 1998, 17, 3996-4003, and J. Am. Chem. Soc. 1998, 120, 6287-6305 new, sterically encumbered fluoroaryl boranes such as tris(perfluorobiphenyl)borane (PBB), and the preparation and use of such compounds as a catalyst for ring opening polymerization of tetrahydrofuran (THF) and as a highly efficient cocatalyst for metallocene-mediated olefin polymerization are described. For example, PBB is a strong organo-Lewis acid which can be synthesized in much higher yield than B(C.sub.6 F.sub.5).sub.3. The anion generated with PBB is non-coordinating instead of being weakly coordinating as in the case of B(C.sub.6 F5).sub.3. Thus, the former exhibits higher catalytic activities and can activate previously unresponsive metallocenes. The catalytically active species generated with PBB are isolable, X-ray crystallographically characterizable instead of the unstable, oily residues often resulting in the case of B(C.sub.6 F.sub.5).sub.4.sup..crclbar.. In addition, PBB exhibits even higher catalytic activities in most cases.
This invention provides, inter alia, technology described in the above-referred-to prior applications, and additionally, improvements in the technology described in the above-referred-to prior applications.